In graphics systems such as television system, a composite signal for a particular frame includes both luma (luminance) and chroma (chrominance/color) data. In order to process the signal, the luma and chroma are separated. The mechanism used to separate the luma and chroma data depends upon the standard with which the signal complies. Typically, however, the mechanism employs either filters or combing. More primitive methods of separating luma and chroma data use the fact that luma and chroma data are predominantly carried at different frequencies. Consequently, the filters pass a particular band of data around the luma or chroma signal.
Other conventional methods use a combing function. In combing, the composite is passed through one or more delays. Each delay provides a delay equivalent to one line. The data in the signal for a line which has been passed through the delay is combined with data for the signal that has not passed through the delay or which has been passed through fewer delays. Depending upon the standard with which the graphics data complies, a the chrominance data for particular line of data is out of phase with the chrominance data for another line of data by a certain amount. For example, in NTSC data, chrominance data for a particular line is 180° out of phase with chrominance data for a neighboring line. In PAL data, chrominance data for a particular line is 90° out of phase with chrominance data for a neighboring line. The signals for different lines are combined to remove chrominance data, leaving luma data. The luma data for a particular line can then be subtracted from the original composite signal to provide the chroma data for the line. Additional signal processing may then be performed in order to improve the separation of luma and chroma data.
Although the conventional mechanisms for separating luma and chroma data functions, one of ordinary skill in the art will readily recognize that errors are often made. In particular, the separation of luma data from chroma data is not complete. As a result, some luma data may be added into portions of the chroma data. Similarly, some chroma data may mistakenly be included in the luma data. Subsequent data processing meant to be performed only on luma or only on chroma data is performed on a mixture of luma and chroma data. When the data are provided for display, therefore, the quality of the image suffers.
Accordingly, what is needed is a system and method for improving the separation of luma data from chroma data in a composite signal. The present invention addresses such a need.